1. Field of the Invention
The present invention relates to a cooking double boiler with which it is possible to easily cook tofu or soymilk skins at home, Japanese style inns, hotels or restaurants.
2. Description of the Prior Art
Tofu or soymilk skins that are made from soymilk are generally produced at factories of tofu makers and are commercially sold at the store of supermarkets and the like. However, accompanying the tofu boom in these years, more and more people make tofu or soymilk skins from soymilk at home. Such homemade tofu or soymilk skins do not contain any preservatives as goods on the marked do, and it is moreover possible to enjoy a freshly made taste. Also when serving tofu for breakfast at Japanese style inns or hotels, it is being preferred to make tofu right before eyes of guests and to serve them in warm conditions.
In this respect, tofu is a food product obtained by curding heated soymilk by a coagulant (magnesium chloride, calcium sulfate or Glucono-delta-lactone etc.) Soymilk skin is a food product, which is a thin film of soy protein that is formed on a surface of soymilk when it is heated without adding bittern thereto, and is eaten by being skimmed therefrom or upon drying the same.
Japanese Utility Patent Registration No. 3,079,181 discloses a pan for manufacturing tofu used for the above purpose. Such a tofu manufacturing pan is comprised of an outer pan, an inner pan with a flange, and a lid that is mounted onto the inner pan. A mixture of a coagulant and soymilk is put into the inner pan, the flange is mounted onto an upper edge of the outer pan, and the top of the inner pan is covered by the lid. When a large amount of water is put into the outer pan and heated, the inner pan is double-boiled, and the soymilk inside thereof is curded to become tofu.
While heating of the soymilk is performed from a bottom surface or sidewalls of the inner pan that are in contact with the hot water within the outer pan in such a tofu manufacturing pan, curding actions are found in soymilk added with a coagulant which results in a gradual increase in viscosity that prevents convection. Accordingly, while heating is performed only through heat transmission through the bottom surface or the sidewalls of the inner pan, a boundary layer of small heat transmission coefficient will be formed at heat transmitting portions so as to remarkably degrade the heat transmission efficiency, and heat will be hardly transmitted to the upper surface or the central portion of the soymilk. The central portion of the soymilk is thus apt to insufficient curding. When the soymilk is heated for a long time for the purpose of curding the upper surface of the central portion thereof, the soymilk that is in contact with the inner pan will be excessively heated so that these curded portions become porous. It was accordingly difficult in a conventional tofu manufacturing pan to uniformly curd the soymilk in the interior thereof.
It is therefore a first object of the present invention to provide a cooking double boiler that enables uniform curding of soymilk and with which everyone can easily make tofu of high quality in a short time.
On the other hand, soymilk skin is a food product that is obtained by heating cold soymilk having a solid content density of 7 to 13% and skimming a curded film that is formed on a surface of this liquid, and similarly to making a tofu, heating operations are also inevitable when forming soymilk skins. However, since the double boiler as disclosed in the above-described Japanese Utility Patent Registration No. 3,079,181 was designed such that the only heat transmitting portion was the bottom portion of the inner pan so that the heat efficiency and the general heat transmission coefficient were small, a drawback was presented in that it took a long time for heating to a temperature suitable for soymilk film formation. Specifically, since it will take 3 to 7 minutes for forming a single soymilk skin and since 4 to 8 sheets are usually skimmed from the same soymilk, it will take as much as approximately 20 to 45 minutes until the last soymilk skin is skimmed off from the point of time the suitable temperature for soymilk skin formation has been reached. Due to the fact that a large amount of fuel is consumed during this time, it was difficult to make soymilk skin by using a small-sized solid fuel, and difficulties were thus found for using such a pan in hotels, restaurants or at home.
Moreover, while it is necessary to supply water since the water within the outer pan was reduced when heating was continued over a long period, it is impossible to supply water without detaching the inner pan in the double boiler as disclosed in the above-described Japanese Utility Patent Registration No. 3,079,181. However, detaching the inner pan containing therein the heated soymilk from the outer pan is dangerous, and the difficulties were found for using such a pan in hotels, restaurants or at home also in this respect.
It is therefore a second object of the present invention to provide a cooking double boiler that does not consume a large amount of fuel and with which everyone can safely make soymilk skim of high quality.